Interpretive Summary: Nitrogen (N) is the most critical element required for plant growth and development and is the basis for fertilizer recommendations. Since a deficiency in N expresses itself in yellowed leaves and stunted growth, recommendations for plant production of floricultural crops are generally based on N requirements. Research has shown the critical amount of N required to produce a marketable plant and, based on symptoms, when additional fertilization is required. What has not been adequately researched is how long a plant can be deprived of sufficient N and still yield a marketable plant. This research was directed at determining how long N could be withheld from production, its impact on plant size, and if a deprived plant could be rescued for sale. Plant size was reduced after just four days of N deprivation but marketable geranium plants could be produced if N was restored for at least 8 days following a period of not longer than 12 days of deprivation. Smaller plants, of similar foliar quality to constantly fed plants, were produced and potentially this manipulation of N supply can be used to control plant growth for marketing purposes.

Technical Abstract:
Nitrogen (N) fertilization recommendations to achieve optimum growth are well established for most floricultural crops. While it has been shown that plant functions can recover from N-deficiency in other crops, little research has investigated the threshold beyond which a bedding plant crop is recoverable. The objective of this research was to determine the effect of N deficiency on geranium chlorophyll content and growth, then to document the degree of recovery and recovery time from N deprivation. This was determined in two experiments by monitoring chlorophyll content and growth of seedlings grown in hydroponic culture in which the N source was removed and then restored after differing lengths of time. Summarizing across both experiments, chlorophyll and foliar N levels were shown to rebound quickly after N depravation; however, growth was reduced after just four days compared to plants fed constantly. Geraniums grown wiithout N for 4 to 12 days resulted in smaller, more compact plants, with lower shoot to root ratios.